The field of the invention is that of ordnance and warhead construction. In particular, the present invention relates to fragmentary warhead construction.
In the prior art, most missile fragmentation warheads either use a solid steel case filled with explosive (which is the conventional design) or consist of explosive surrounded by a thin shell with "discrete" fragments glued to the shell which is generally called the discrete fragment design. In either case the warhead is then mounted into the ordnance section where structural loads are carried by a surrounding shroud.
An example of the conventional steel case design is LaRocca, U.S. Pat. No. 3,799,054 filed Mar. 26, 1974. This reference teaches a warhead for controlling the fragmentation of explosive devices having a cylindrical metallic fragmentation casing, wrapped with metallic strips of heavy density to cause fragments to form. This type of construction employs heavy construction materials which, by necessity, must be massive in areas that optimum airframe design would dictate a lighter or different design. This conventional warhead highlights the design tension between fragmentation and structural integrity. Generally a missile airframe demands light, strong materials, and warhead fragments need to be heavy, close tolerance, objects. Methods for achieving uniform fragmentation are generally not consistent with good airframe design.
In small missiles it is conventional for the warhead case to double as both the fragmentation panel and the load bearing member of the airframe. This engenders a conflict between the need for strength in the load bearing member and the need to score this member to form fragments. Alternate methods of forming fragments, using discrete pellets, require subcaliber techniques which lower lethality and require the fragments to blow through the metallic shroud material, which further degrades kill performance.
An example of discrete fragment design is represented by Brumfield et al., U.S. Pat. No. 3,977,327 filed Aug. 31, 1976. The Brumfield et al. reference is typical of many fragmentation schemes which precut fragments and then sandwich them between steel/aluminum cylinders to form the case or missile airframe. The required airframe structure then becomes parasitic weight from a warhead design perspective.
In a like manner, both the discrete fragment and the conventional designs share a common flaw from the overall system perspective. In both designs the warhead is usually carried as parasitic weight within a surrounding missile shroud. There are two drawbacks to this. First, the warhead is forced to "blow" through the shroud. Having to do this degrades fragment breakup as well as fragment velocity. Second, to minimize fragment degradation the missile shroud is made as thin and light as possible in the blow through area thereby reducing the shroud's structural integrity.
This parasitic weight issue can be alleviated to some degree by utilizing an integral warhead with a removable explosive assembly. However, this option suffers from an inability to customize fragmentation and from a weight penalty caused by using steel shroud.
Another recent concern in the warhead arts is the development of warheads that are safe to carry on our nation's ships and aircraft. These concerns are reflected in the new insensitive munitions requirements which became effective to all naval munitions in 1987. One of these requirements is that a warhead survive a fire or high heat environment without exploding. The steel or metallic case warheads do not allow the venting necessary so that the explosive mix burns rather than explodes. Elaborate cook-off plugs and other schemes to allow venting further degrade the case integrity and further reduce strength.
The disadvantages of the conventional design and the discrete fragment design are overcome by the present invention which provides a lightweight warhead case that integrates into the missile as a load bearing section without adding parasitic weight or degrading lethality, while still exhibiting the advantages of discrete fragments and safety.